Mutations Amd Gene Expression

Question 1

What is a mutation?

Answer 1

A mutation is any change to the base sequence of DNA. This can be caused by errors in DNA replication.

Question 2

What are the 6 different types of mutation?

Answer 2

Substitution - 1+ swapped for another
Addition - 1+ added
Deletion - 1+removed
Duplication - 1+ repeated
Inversion - when a sequence of bases is reversed
Translocation - moved from one location to another

Question 3

What does the order of DNA bases determine? What happens if a mutation occurs?

Answer 3

The DNA base sequence determines the Amino Acid sequence of a polypeptide.
A mutation would cause a change in the A.A sequence of the P.P.
This may change the final 3D shape of the protein
This could mean it doesn’t work properly

Question 4

What can mutations cause?

Answer 4

Genetic disorders (inherited disorders caused by abnormal genes)
Increased likelihood of developing certain cancers.

Question 5

What are hereditary mutations?

Answer 5

These are when the mutation is passed on to the offspring

When a gamete containing a mutation for a genetic disorder is fertilised, the mutation will be present in the new fetus

Question 6

Why is it that not all mutations will result in a change in the AA sequence of the PP

Answer 6

Due to the degenerate nature of the DNA code, some AAs are coded for by more than one triplet. (common in substitutions)

Question 7

Which types of mutations will al OST always change the AA sequence of a PP? How?

Answer 7

Additions, duplications and deletions
This is because they change the number of bases in the DNA code, causing a FRAMESHIFT in the base triplets that follow
And so the triplet code is read differently.

Question 8

What is a mutagenic agent?

Answer 8

A mutagenic agent is something that increases the rate of mutations.

Question 9

How does a mutagenic agent perform their function by acting as a base?

Answer 9

Chemicals called base analogs can substitute for a base in DNA replication, changing the base sequence in the new DNA

Question 10

How does a mutagenic agent perform its function by altering bases?

Answer 10

Some chemicals can delete of alter bases.

E.g. alkylating agents can add an alkyl group to guanine, which changes the structure making it pair with T instead if C

Question 11

How does a mutagenic agent perform its function by altering the structure of DNA?

Answer 11

Some types of radiation can change the structure of DNA, causing problems in DNA replication.
E.g. UV radiation can cause adjacent thymine bases to pair up together.

Question 12

What is an acquired mutation? How can they cause uncontrolled cell division?

Answer 12

Acquired mutations are mutations that occur in individual cells after fertilisation.
If these mutations occur in the genes that control the rate of cell division, it causes uncontrolled cell division.

Question 13

What is the result of a cell dividing uncontrollably?

Answer 13

A tumour- a mass of abnormal cells.

Question 14

What is a cancer?

Answer 14

A tumour that invades and destroys surrounding tissue.

Question 15

Mutations in a tumour suppressor gene causes cancer. How?

Answer 15

When functioning normally, TSGs slow cell division by producing proteins that stop cells dividing or cause them to self destruct.
If a mutation occurs, the TSG can be inactivated, meaning the protein isn’t produced and so the cells divide uncontrollably = tumour.

Question 16

Mutations in a proto-oncogene causes cancer. How?

Answer 16

When functioning normally, P-Os stimulate cell division by producing proteins that make cells divide.
If a mutation occurs in a P-O, the gene can become overactive. This stimulates the cell to divide uncontrollably = tumour.

Question 17

What are the two different types of tumour?

Answer 17

MALIGNANT- Cancerous. Grow rapidly and invade/ destroy surrounding tissue. Cells can break off and spread to other parts of the body in the blood stream.
BENIGN- not cancerous. Glow slower. Often covered in fibrous tissue to stop it spreading. Harmless, but Catie blockages and put pressure on organs. Some benign tumours can become malignant.

Question 18

How do tumour cells differ from normal cells?

Answer 18

Irregular shape
Nucleus larger and darker
Don’t produce all the proteins needed for functioning correctly
Have different antigens on their surface
Don’t respond to growth regulating processes
Divide quicker than normal cells.

Question 19

What is methylation? Why is it important in gene expression?

Answer 19

Methylation is adding a methyl group onto something. Important method of regulating gene expression by controlling whether or not a gene is transcribed and translated.

Question 20

When is methylation a problem?

Answer 20

When it happens too much - hypERmethylation

When it happens too little - hypOmethylation

Question 21

How is the growth of tumours caused by abnormal methylation of certain cancer related genes?

Answer 21

When TSGs are hypERmethylated, the genes aren’t transcribed and so the proteins they produce to slow cell division aren’t produced.
HypOmethylation of P-Os causes them to act as oncogenes - increasing the production of proteins that stimulate cell division.

Question 22

What is the effect of oestrogen on breast cancer?

Answer 22

Increased exposure to oestrogen after an extended period of time is thought to increase a woman’s risk of developing breast cancer.

Question 23

What are the theories behind oestrogen increasing risk of breast cancer?

Answer 23

Oestrogen can stimulate certain breast cells to divide and regulate. More cell divisions = naturally increases the chance of mutations = increases chance of cells being cancerous.
The ability to stimulate division means that if a cell becomes cancerous, replication could be assisted by oestrogen.
Other research suggests oestrogen is actually able to introduce mutations directly into the DNA of certain breast cells - increases the chance of these cells becoming cancerous.